Coupling of glycerol processing with Fischer–Tropsch synthesis for production of liquid fuels

Abstract

Liquid alkanes can be produced directly from glycerol by an integrated process involving catalytic conversion to H₂/CO gas mixtures (synthesis gas) combined with Fischer–Tropsch synthesis. Synthesis gas can be produced at high rates and selectivities suitable for Fischer–Tropsch synthesis (H₂/CO between 1.0 and 1.6) from concentrated glycerol feed solutions at low temperatures (548 K) and high pressures (1–17 bar) over a 10 wt% Pt–Re/C catalyst with an atomic Pt : Re ratio of 1 : 1. The primary oxygenated hydrocarbon intermediates formed during conversion of glycerol to synthesis gas are ethanol, acetone, and acetol. Fischer–Tropsch synthesis experiments at 548 K and 5 bar over a Ru-based catalyst reveal that water, ethanol, and acetone in the synthesis gas feed have only small effects, whereas acetol can participate in Fischer–Tropsch chain growth, forming pentanones, hexanones, and heptanones in the liquid organic effluent stream and increasing the selectivity to C₅₊ alkanes by a factor of 2 (from 0.30 to 0.60). Catalytic conversion of glycerol and Fischer–Tropsch synthesis were coupled in a two-bed reactor system consisting of a Pt–Re/C catalyst bed followed by a Ru/TiO₂ catalyst bed. This combined process produced liquid alkanes with S_C5+ between 0.63 and 0.75 at 548 K and pressures between 5 and 17 bar, with more than 40% of the carbon in the products contained in the organic liquid phase at 17 bar. The aqueous liquid effluent from the integrated process contains between 5 and 15 wt% methanol, ethanol, and acetone, which can be separated from the water by distillation and used in the chemical industry or recycled for conversion to gaseous products. This integrated process has the potential to improve the economics of “green” Fischer–Tropsch synthesis by reducing capital costs and increasing thermal efficiency. Importantly, the coupling between glycerol conversion to synthesis gas and Fischer–Tropsch synthesis leads to synergies in the operations of these processes, such as (i) avoiding the highly endothermic and exothermic steps that would result from the separate operation of these processes and (ii) eliminating the need to condense water and oxygenated hydrocarbon byproducts between the catalyst beds.